Stiction
Friction can hold the valve in place while the command changes, followed by a sudden movement when it breaks free. Compare the response with operating conditions before attributing the behaviour to packing or another component.
What to check
- 01Compare command and travel during opening and closing.
- 02Look for repeated sticking and release under comparable conditions.
- 03Check packing, linkage, actuator and positioner condition before selecting a repair.
Illustrative example.
96%
Example · Detection rate
6–10 wks
Example · Lead time
+31%
Example · Friction, 90 d
€48k
Example · Loss avoided
Deadband
After a change in direction, the command may change before valve travel responds. Review the response and mechanical condition to distinguish lost motion from other sources of delayed movement.
What to check
- 01Compare the response in each direction.
- 02Check whether delayed movement repeats under comparable demand.
- 03Inspect the linkage and review positioner settings before attributing the cause.
Illustrative example.
93%
Example · Detection rate
8 wks
Example · Lead time
2.2 → 3.4%
Example · Deadband
1.4×
Example · Variability
Positioner drift
A persistent difference between command and reported position warrants investigation. Check calibration and the position measurement before treating the difference as a mechanical fault.
What to check
- 01Compare command and position across the operating range.
- 02Review calibration records and signal quality.
- 03Verify actual travel before deciding whether calibration or mechanical inspection is needed.
Illustrative example.
95%
Example · Detection rate
2 wks
Example · Lead time
3.1%
Example · Zero offset
None
Example · Extra hardware
Diaphragm & spring issue
A slow or incomplete stroke can warrant an actuator check. Command and travel data can guide the investigation, but cannot by themselves confirm a damaged diaphragm or weakened spring.
What to check
- 01Compare stroke response under comparable demand.
- 02Review the actuator supply and available diagnostic data.
- 03Use an approved inspection or test procedure to verify diaphragm, spring and fail-safe condition.
Illustrative example.
91%
Example · Detection rate
3–5 wks
Example · Lead time
+18%
Example · Stroke time
0.4 bar
Example · Hold decay
Controller performance
Compare Command Output with Position Feedback to describe overshoot, undershoot or hunting. These response patterns guide an investigation; they do not establish the cause or a repair deadline on their own.
Overshoot
Illustrative response — synthetic example, not measured plant data.
What it means. Control overshoot occurs when Position Feedback moves beyond the commanded setpoint before the control system brings it back to the desired position.
What can contribute. High gain or sensitivity, low damping, disturbances or noise, and wear in the valve or related components can all contribute.
Repeated overshoot can increase process variability and develop into unstable oscillation. The response pattern guides investigation; it does not prove one cause.Undershoot
Illustrative response — synthetic example, not measured plant data.
What it means. Control undershoot occurs when Position Feedback initially falls short of the commanded setpoint before recovering toward the desired position.
What can contribute. Its causes can overlap with overshoot, including tuning or gain, low damping, disturbances, friction, and mechanical condition.
Persistent undershoot means the valve is not delivering the requested travel when it is first needed. Compare the complete response before assigning a root cause.Hunting
Illustrative response — synthetic example, not measured plant data.
What it means. Hunting is repeated oscillation around a stable setpoint: Position Feedback keeps crossing the target while the controller continues to correct.
What can contribute. Poor tuning, high gain, low damping, process disturbances, noise, friction, or component wear may sustain the oscillation.
Hunting creates an unstable, unpredictable response that is harder to maintain and optimise. Diagnose the contributing mechanism before changing tuning or hardware.Illustrative example.
89%
Example · Detection rate
3 mo
Example · Lead time
−7%
Example · Cv at 60% travel
€120k
Example · Loss avoided
A finding, the supporting evidence and the next check.
Bring the observed response, possible causes and required checks together. Maintenance scope and timing should follow a verified diagnosis and the site operating requirements.
Use the evidence to decide whether the valve needs calibration, inspection or repair. Cost and downtime estimates should come from the confirmed work scope and site records.
